The power of flowers

BySharon J. HuntingtonJuly 8, 2003

Do you have a favorite flower? You might like some flower best because of its color or smell or shape. If so, you're not alone. Animals and insects have favorite blooms, too. That's part of the reason there are so many different flowers. Each one is designed to attract a particular pollinator.

Flowers create new flowers through pollination. The pollen from one flower has to get to another flower of the same species to create seeds. Often the pollen is transferred by insect or animal. So flowers put on their best dress and fanciest perfume to attract their special pollinator. They even offer visitors a reward.

Some flowers are best pollinated by bees, and bees don't see colors the way we do. They see blue and yellow colors best. Reds are very dull to them. So flowers that want to attract bees have blue or yellow blossoms. Bees can also see ultraviolet markings. So some flowers have "honey guides," ultraviolet lines that serve as a landing pattern to guide bees to the flower's nectar. The bee is rewarded for landing by receiving nectar, which it uses for food. As it brushes against the flower's stamens, where its pollen is, some of it rubs off onto the insect's body. The pollen then rubs off onto other flowers as the bee continues gathering nectar. (Honeybees also collect pollen, which they use for food.)

Smell is also used to attract pollinators. Most bee-attracting flowers have a light, sweet scent. Butterflies don't have a good sense of smell. So many of the blossoms that attract butterflies don't have a strong odor. Flies, on the other hand, are attracted to smells we consider pretty awful. If you've ever taken a whiff of a voodoo lily, it might have reminded you of a cow barn. The blackish leaves even look a little like rotting flesh. That says "dinner!" to a fly.

One of the sneakiest flowers is the ophrys orchid. It looks and even smells like a female wasp. Male wasps fly into orchid after orchid looking for a date, spreading pollen from flower to flower.

Bat-pollinated flowers usually produce strong fruity or musky scents. These flowers are often night-bloomers, because that's when bats are active. Moths also feed at night, so moth-pollinated flowers are white or pale colors so they are visible at night. The blooms may only be open at night and have very heady, sweet fragrances, which moths love.

Shape can also be important in attracting pollinators. Long, tubular blossoms attract the hummingbird. Its long beak and tongue reach far inside a flower to get the nectar. As it does, the bird's head bumps into the flower's stamens, collecting pollen to transfer to the next flower. Some flowers, such as the hibiscus, have blossoms that point downward. Only a hovering bird like the hummingbird can hang below the flower and reach upward into the blossom. The tillandsia flower points upward to attract perching birds. It has stiff leaves to support the weight of a bird.

A flower's structure can also help improve pollination. The mountain laurel grows 10 stamens on long filaments. Before the flower blooms, these filaments bend to fit inside the bud. When the flower blooms, the 10 filaments are like springs waiting to be set off. An insect landing near the center of the bloom sets the filaments loose. It gets whacked with 10 stamens and covered with pollen.

Some flowers are very specialized about the pollinators they permit. Snapdragons must be opened before the insect can reach the nectar inside. When a bumblebee lands on the flower, its weight opens the flower. Smaller bees aren't heavy enough to do the job. (A bed of snapdragons is a good place to see bumblebees in action.)

Moths tend to hover while feeding. Some moth-pollinated plants have tubular blossoms exactly the length of the moth's tongue that pollinates them. In fact, when 19th-century naturalist Charles Darwin examined the Star of Bethlehem orchid on Madagascar, he hypothesized the existence of a moth with a 12-inch-long proboscis (long, curled tongue), which the insect would need to reach the flower's nectar. That moth was discovered 40 years later.

Whether a flower accepts only one pollinator or a variety of visitors, each flower has developed a color, shape, and smell to appeal to the pollinator it needs. And that gives us humans a wide variety of beautiful blossoms to enjoy as well.

The materials that create colors in flowers, as well as in animals and humans, are called pigments. Chlorophyll pigment produces the green color of leaves and stems. Carotene produces yellow and orange colors in flowers, cantaloupes, and sweet potatoes. (It was first discovered in carrots, hence its name.) Other yellow and orange flowers, such as marigolds, get their colors from xanthophyll pigments.

Flowers that appear black are often a very deep purple, or a combination of purple and green pigments. Red, blue, and purple flowers are tinted by anthocyanin pigments. So are strawberries, apples, and plums.

Gardeners can sometimes change the color of a flower by adding something to the soil that alters the amount of pigment in the flower. For example, if you add lime to the soil around a blue hydrangea, it will turn pink. You can explore how these colors change with this experiment:

You will need petals from several dark blue or purple flowers (pansies or irises, perhaps), white vinegar, and baking soda. You'll also need two small bowls, an eyedropper, a teaspoon, a microwave oven, and a microwave-safe bowl.

Have an adult help you heat a cup of water in a microwave-safe bowl until it boils. Drop in the petals and boil for another 1 or 2 minutes. Use a spoon to remove the petals. The water should now be dark blue or purple. You have taken the anthocyanin pigment from the petals and dissolved it in the water. Let the water cool a little, then pour it into two small bowls.

Put a few drops of vinegar in one bowl. The acid in the vinegar will turn the water more red. Now put some baking soda in the other bowl and stir. The alkaline soda will turn the water a deeper blue.

The anthocyanin pigment in flower petals can mix with liquids in the sap to change the color of the flowers. (Carotene pigments don't dissolve in the sap, so this experiment won't work with yellow or orange flowers.)

SOURCE: This experiment is adapted from 'Roses Red, Violets Blue: Why Flowers Have Colors,' by Sylvia A. Johnson, Lerner Publication Co., 1991. The book is an English translation edition of the Japanese title by Yukoh Sato, published by Akane Shobo Co.; the experiment is used with permission.

Whose favorites are these?

For each flower described, select the pollinators above that it will best attract. Note: There may be more than one. (Answers below.)

A. Painted Daisy

Besides the red and yellow humans can see, ultraviolet patterns are also present, which attract the pollinators.

B. Milkweed

The pollinator must grasp the stalk and keep its large wings back while getting the nectar. Pollen sacs have a type of 'super glue' to stick to the insect's legs before it flies off.

C. Snapdragon

It takes an insect of a special weight to open this bloom and reach the nectar inside.

D. Firecracker flower

The long, tubular blooms of this plant attract a hovering pollinator with a long beak.

E. White night-blooming honeysuckle

These heavily fragrant blossoms are perfectly suited to pollinators with long, curled tongues.

F. Cactus

These bloom in the cool of the night, when their pollinators leave their caves to look for food.

G. columbine

A pollinator must hover below this blossom to reach the nectar within it.